Method for supporting efficient PDU session activation and deactivation in cellular networks

ABSTRACT

A communication method and system converges a 5G communication system for supporting higher data rates beyond a 4G system with an IoT technology. The system and method may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. Embodiments provide a scheme for efficiently operating an UP connection of a session in case where a terminal has a plurality of sessions in a mobile communication system, such as a 5G system, having a network structure in which an AMF for mobility management and an SMF for session management are separated from each other. A terminal (UE) can optimize a non-access stratum (NAS) signaling message, and can perform data transmission/reception with low latency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 16/817,501,filed Mar. 12, 2020, which is a continuation of application Ser. No.16/673,629, filed Nov. 4, 2019, now U.S. Pat. No. 10,595,294, which is acontinuation of application Ser. No. 16/368,360, filed Mar. 28, 2019,now U.S. Pat. No. 10,470,153, which is a continuation of applicationSer. No. 15/926,953, filed Mar. 20, 2018, now U.S. Pat. No. 10,251,147,which claims priority to Korean Patent Application No. 10-2017-0034671,filed Mar. 20, 2017 and Korean Patent Application No. 10-2017-0100159,filed Aug. 8, 2017, the disclosures of which are incorporated herein byreference in its entirety.

BACKGROUND 1. Field

The present disclosure relates to a method for efficiently managing anUP connection resource of a PDU session in a cellular wirelesscommunication system.

2. Description of Related Art

In order to meet the demand for wireless data traffic that is on anincreasing trend after commercialization of 4G communication systems,efforts have been made to develop improved 5G or pre-5G communicationsystem. For this reason, the 5G or pre-5G communication system is alsocalled a beyond 4G network communication system or a post LTE system. Inorder to achieve high data rate, implementation of a 5G communicationsystem in an ultrahigh frequency (mmWave) band (e.g., like 60 GHz band)has been considered.

In order to mitigate a path loss of radio waves and to increase atransfer distance of the radio waves in the ultrahigh frequency band,technologies of beamforming, massive MIMO, full dimension MIMO(FD-MIMO), array antennas, analog beamforming, and large scale antennasfor the 5G communication system have been discussed. Further, for systemnetwork improvement in the 5G communication system, technologydevelopments have been made for an evolved small cell, advanced smallcell, cloud radio access network (cloud RAN), ultra-dense network,device to device communication (D2D), wireless backhaul, moving network,cooperative communication, coordinated multi-points (CoMP), andreception interference cancellation. In addition, in the 5G system,hybrid FSK and QAM modulation (FQAM) and sliding window superpositioncoding (SWSC), which correspond to advanced coding modulation (ACM)systems, and filter bank multicarrier (FBMC), non-orthogonal multipleaccess (NOMA), and sparse code multiple access (SCMA), which correspondto advanced connection technologies, have been developed.

On the other hand, the Internet, which is a human centered connectivitynetwork where humans generate and consume information, is now evolvingto the Internet of things (IoT) where distributed entities, such asthings, exchange and process information. The Internet of everything(IoE), which is a combination of the IoT technology and big dataprocessing technology through connection with a cloud server, hasemerged. As technology elements, such as sensing technology,wired/wireless communication and network infrastructure, serviceinterface technology, and security technology, have been demanded forIoT implementation, a sensor network for machine-to-machine connection,machine-to-machine (M2M) communication, machine type communication(MTC), and so forth have been recently researched.

Such an IoT environment may provide intelligent Internet technology (IT)services that create a new value to human life by collecting andanalyzing data generated among connected things. The IoT may be appliedto a variety of fields including smart home, smart building, smart city,smart car or connected cars, smart grid, health care, smart appliancesand advanced medical services through convergence and combinationbetween the existing information technology (IT) and various industries.

Accordingly, various attempts have been made to apply the 5Gcommunication system to IoT networks. For example, technologies ofsensor network, machine to machine (M2M) communication, and machine typecommunication (MTC) have been implemented by techniques forbeam-forming, MIMO, and array antennas, which correspond to the 5Gcommunication technology. As the big data processing technology asdescribed above, application of a cloud radio access network (cloud RAN)would be an example of convergence between the 5G technology and the IoTtechnology.

On the other hand, in order to achieve evolution from the existing 4GLTE system into the 5G system, 3GPP that takes charge of the cellularmobile communication standard has named a new core network structure a5G core (5GC) and has proceeded with the standardization thereof.

As compared with an evolved packet core (EPC) that is an existing 4Gnetwork core, the 5GC supports the following discriminated functions.The first is introduction of a network slice function. As the 5Crequirements, the 5GC should support various types of terminals andservices: e.g., enhanced mobile broadband (EMBB), ultra-reliable lowlatency communications (URLLC), and massive machine type communications(mMTC). Such terminals/services have different requirements used inrespective core networks. For example, in case of an eMBB service, highdata rate may be used, whereas in case of a URLLC service, highstability and low latency may be used.

A technology proposed to satisfy such various service requirements is anetwork slice scheme. Network slice is a method for virtualizing onephysical network to make several logic networks, and respective networkslice instances (NSIs) may have different characteristics. This becomespossible by making the respective NSIs have network functions (NF) thatsuit the characteristics. Several 5G services can be efficientlysupported by allocating to terminals the NSIs that suit thecharacteristics of services used for the respective terminals.

The second may be easiness in network virtualization paradigm supportthrough separation between a mobility management function and a sessionmanagement function. In the existing 4G LTE, all terminals can beprovided with services in a network through signaling exchange withsingle-core equipment that is called a mobility management entity (MME)taking charge of registration, authentication, mobility management, andsession management functions. However, in the 5G, since the number ofterminals is explosively increased, and mobility and traffic/sessioncharacteristics to be supported are subdivided in accordance withterminal types, scalability to add entities for necessary functions islowered in case where all functions are supported by the singleequipment such as the MME. Accordingly, in order to improve thescalability in function/implementation complexity of the core equipmenttaking charge of control plane and signaling load, various functionshave been developed based on a structure for separating the mobilitymanagement function and the session management function from each other.

FIG. 1 illustrates a network architecture for a 5G system. An access andmobility management function (AMF) of managing terminal mobility andnetwork registration and a session management function (SMF) of managingan end-to-end session are separated from each other, and may send andreceive signaling through an N11 interface.

Third, a 5G terminal may set up a plurality of packet data unit (PDU)sessions for data communication with one data network name (DNN) such asInternet. Accordingly, the 5G terminal supports a function of making andremoving UP connection (i.e., data radio bearer+N3 tunnel) between aterminal (UE) and a core network (CN) independently for respective PDUsessions.

Basically, if a terminal goes to a CM-IDLE state, it releases the UPconnection of all PDU sessions. The terminal in the CM-IDLE stateremakes only the UP connection of the PDU session to whichmobile-originated (MO) or mobile-terminated (MT) traffics belong whenreturning again to a CM-CONNECTED state due to the mobile-originated(MO) or mobile-terminated (MT) traffics.

The terminal in the CM-CONNECTED state may perform an activationprocedure of additionally making the UP connection with respect to thePDU session in which the UP connection has not yet been made. Further,the terminal in the CM-CONNECTED state can maintain only the UPconnection of the PDU session in which the traffic occurs by performinga procedure of deactivating the UP connection of the activated PDUsession through the network entity (e.g., AMF or SMF) of the corenetwork, and thus UP connection resources can be saved. By independentlyactivating the UP connection of the PDU session as described above, thesignaling and UP connection resources can be additionally saved when theterminal performs a handover.

SUMMARY

An aspect of the present disclosure proposes a method for activating anUP connection resource of a specific PDU session in accordance withwhether NAS signaling is connected between a terminal and an AMF duringmanagement of UP connection resources of independent (or selective) PDUsessions, and also proposes a method for a terminal in a CM-IDLE stateto efficiently operate an N9 tunnel of the PDU session including aplurality of UPFs.

In accordance with an aspect of the present disclosure, a method by asession management function (SMF) entity for managing a protocol dataunit (PDU) session in a wireless communication system includestransmitting a first message requesting a location change notificationfor a terminal in an idle state to an access and mobility managementfunction (AMF) entity; receiving a second message including informationon a changed location of the terminal from the AMF entity; anddetermining whether to maintain at least one of a plurality of userplane functions (UPFs) included in the PDU session for the terminalbased on the second message.

In accordance with another aspect of the present disclosure, a method byan access and mobility management function (AMF) entity for managing aprotocol data unit (PDU) session in a wireless communication systemincludes receiving a first message requesting a location changenotification for a terminal in an idle state from a session managementfunction (SMF) entity; and transmitting a second message includinginformation on a changed location of the terminal to the SMF entitybased on the first message if the location change of the terminal isdetected, wherein the second message is used to determine whether tomaintain at least one of a plurality of user plane functions (UPFs)included in the PDU session for the terminal by the SMF entity.

In accordance with still another aspect of the present disclosure, asession management function (SMF) entity in a wireless communicationsystem includes a transceiver configured to transmit a first messagerequesting a location change notification for a terminal in an idlestate to an access and mobility management function (AMF) entity; and acontroller configured to control the transceiver to receive a secondmessage including information on a changed location of the terminal fromthe AMF entity and to determine whether to maintain at least one of aplurality of user plane functions (UPFs) included in a protocol dataunit (PDU) session for the terminal based on the second message.

In accordance with yet still another aspect of the present disclosure,an access and mobility management function (AMF) entity in a wirelesscommunication system includes a transceiver configured to receive afirst message requesting a location change notification for a terminalin an idle state from a session management function (SMF) entity; and acontroller configured to control the transceiver to transmit a secondmessage including information on a changed location of the terminal tothe SMF entity based on the first message if the location change of theterminal is detected, wherein the second message is used to determinewhether to maintain at least one of a plurality of user plane functions(UPFs) included in a protocol data unit (PDU) session for the terminalby the SMF entity.

According to the aspect of the present disclosure, the terminal (UE) canoptimize a non-access stratum (NAS) signaling message, and can performdata transmission/reception with low latency. Further, if the MT or MOtraffic occurs in a state where the terminal is in the CM-IDLE state,rapid data transmission becomes possible with respect to the PDU sessionin which the UP connection has already been set up.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.

Moreover, various functions described below can be implemented orsupported by one or more computer programs, each of which is formed fromcomputer readable program code and embodied in a computer readablemedium. The terms “application” and “program” refer to one or morecomputer programs, software components, sets of instructions,procedures, functions, objects, classes, instances, related data, or aportion thereof adapted for implementation in a suitable computerreadable program code. The phrase “computer readable program code”includes any type of computer code, including source code, object code,and executable code. The phrase “computer readable medium” includes anytype of medium capable of being accessed by a computer, such as readonly memory (ROM), random access memory (RAM), a hard disk drive, acompact disc (CD), a digital video disc (DVD), or any other type ofmemory. A “non-transitory” computer readable medium excludes wired,wireless, optical, or other communication links that transporttransitory electrical or other signals. A non-transitory computerreadable medium includes media where data can be permanently stored andmedia where data can be stored and later overwritten, such as arewritable optical disc or an erasable memory device.

Definitions for certain words and phrases are provided throughout thispatent document. Those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 is a diagram illustrating a network structure of a 5G system andan interface;

FIG. 2 is a diagram illustrating a network structure in case where aterminal sets up a plurality of PDU sessions including a PDU sessioncomposed of a plurality of UPFs through a 5G network;

FIG. 3 is a diagram illustrating a network structure of a 5G system andan interface for providing a home-routed roaming service;

FIG. 4 is a diagram illustrating a network structure of a 5G system andan interface for providing a local breakout roaming service;

FIG. 5 is a diagram illustrating a network structure in case where aterminal sets up three PDU sessions according to an embodiment;

FIG. 6 is a diagram illustrating information managed by an AMF for eachPDU session of a terminal according to an embodiment;

FIG. 7 is a diagram illustrating an operation of an SMF related to anindication for synchronization/asynchronization with a NAS signalingconnection for each PDU session according to an embodiment;

FIG. 8 is a diagram illustrating an operation of an AMF related to anindication for synchronization/asynchronization with a NAS signalingconnection for each PDU session according to an embodiment;

FIG. 9 is a diagram illustrating an operation of a terminal (UE) relatedto an indication for synchronization/asynchronization with a NASsignaling connection for each PDU session according to an embodiment;

FIG. 10 is a diagram illustrating an operation of an AMF related to anindication for synchronization/asynchronization with a NAS signalingconnection when the NAS signaling connection between a terminal and theAMF is released according to an embodiment;

FIG. 11 is a diagram illustrating an operation of an AMF related to anindication for synchronization/asynchronization with a NAS signalingconnection when the NAS signaling connection between a terminal and theAMF is set up according to an embodiment;

FIG. 12 is a diagram illustrating an operation of a terminal in aCM-IDLE state related to an indication forsynchronization/asynchronization with a NAS signaling connectionaccording to an embodiment;

FIG. 13 is a diagram illustrating an operation performed by an SMF incase where a plurality of UPFs participate in a process in which aterminal sets up a PDU session according to an embodiment;

FIG. 14 is a diagram illustrating an operation of an SMF in case where aterminal in a CM-IDLE state receives a notification on locationinformation of the terminal from an AMF according to an embodiment;

FIG. 15 is a diagram illustrating an operation of an AMF in case wherethe AMF receives a notification on UE location change from an SMFaccording to an embodiment;

FIG. 16 is a diagram illustrating an operation of an SMF in case wherethe SMF receives a PDU session activation request from an AMF accordingto an embodiment;

FIG. 17 is a diagram illustrating a case where a plurality of UPFs areincluded in a PDU session establishment procedure by a terminalaccording to an embodiment;

FIG. 18 is a diagram illustrating an operation for releasing an N9tunnel with respect to a PDU session composed of a plurality of UPFsaccording to an embodiment;

FIG. 19 is a diagram illustrating an operation for changing an N9 tunnelwith respect to a PDU session composed of a plurality of UPFs accordingto an embodiment;

FIG. 20 is a diagram illustrating an operation for releasing an N9tunnel in case where an SMF receives a trigger condition for releasingthe N9 tunnel with respect to a PDU session composed of a plurality ofUPFs according to an embodiment.

FIG. 21 is a block diagram illustrating the SMF in a network accordingto an embodiment of the present invention.

FIG. 22 is a block diagram illustrating the AMF in the network accordingto an embodiment of the present invention.

FIG. 23 is a block diagram illustrating the terminal in the networkaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

FIGS. 1 through 20, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged system or device

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings. In describing thepresent disclosure, a detailed description of related known functions orconfigurations will be omitted if it is determined that it obscures thedisclosure in unnecessary detail. Further, all terms used in thedescription are general terms that are widely used in consideration oftheir functions in the present disclosure, but may differ depending onintentions of a person skilled in the art to which the presentdisclosure belongs, customs, or appearance of new technology.Accordingly, they should be defined based on the contents of the wholedescription of the present disclosure.

The aspects and features of the present disclosure and methods forachieving the aspects and features will be apparent by referring to theembodiments to be described in detail with reference to the accompanyingdrawings. However, the present disclosure is not limited to theembodiments disclosed hereinafter, but can be implemented in diverseforms. The matters defined in the description, such as the detailedconstruction and elements, are nothing but specific details provided toassist those of ordinary skill in the art in a comprehensiveunderstanding of the disclosure, and the present disclosure is onlydefined within the scope of the appended claims. In the entiredescription of the present disclosure, the same drawing referencenumerals are used for the same elements across various figures.

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings. In describing thepresent disclosure, a detailed description of related known functions orconfigurations will be omitted if it is determined that it obscures thedisclosure in unnecessary detail. Further, all terms used in thedescription are general terms that are widely used in consideration oftheir functions in the present disclosure, but may differ depending onintentions of a person skilled in the art to which the presentdisclosure belongs, customs, or appearance of new technology.Accordingly, they should be defined based on the contents of the wholedescription of the present disclosure.

Hereinafter, a base station is a subject that performs resourceallocation to a terminal, and may be at least one of an eNode B, Node B,base station (BS), radio access network (RAN), access network (AN),radio connection unit, base station controller, and node on a network. Aterminal may include user equipment (UE), mobile station (MS), cellularphone, smart phone, computer, or multimedia system capable of performinga communication function. In the present disclosure, a downlink (DL) isa radio transmission path of a signal that is transmitted from the basestation to the terminal, and an uplink (UL) means a radio transmissionpath of a signal that is transmitted from the terminal to the basestation.

Although embodiments of the present disclosure will be describedhereinafter as being exemplified through an LTE or LTE-A system, theycan also be applied to other communication systems having similartechnical backgrounds or channel types. Further, the embodiments of thepresent disclosure may also be applied to other communication systemsthrough partial modifications thereof in a range that does not greatlydeviate from the scope of the present disclosure through the judgment ofthose skilled in the art.

The present disclosure provides a scheme for determining whether to makean UP connection of a PDU session in accordance with a NAS signalingconnection state (defined as CM-IDLE or CM-CONNECTED state) between aterminal and an AMF by defining an attribute of the PDU session used asa data transmission path in a cellular network. Further, the presentdisclosure provides a scheme for determining whether to maintain orrelease an N9 tunnel between a terminal and a UPF when the terminal in aCM-IDLE state moves if a plurality of user plane functions (UPFs) areincluded in a specific PDU session.

Specifically, an indication for synchronization/asynchronization withthe NAS signaling connection may be introduced as an attribute of thePDU session. The indication may be determined by an SMF in a PDU sessionestablishment procedure. In the establishment procedure, the AMF storesassociation between a PDU session ID and a serving SMF ID together withan indication for synchronization/asynchronization with the NASsignaling connection for each PDU session.

For example, if the indication of a specific PDU session is ON (orexists), a procedure of setting up the UP connection of the PDU sessionmay be accompanied when the NAS signaling connection is set up (entersinto a CM-CONNECTED state). On the other hand, if the indication of thespecific PDU session is OFF (or does not exist), the procedure ofsetting up the UP connection of the PDU session may not be accompaniedeven if the NAS signaling connection is set up. In this case, the UPconnection of the PDU session is set up only in case where the trafficusing the PDU session occurs.

When the PDU session establishment is completed, and a PDU sessionestablishment accept message is transferred to the terminal, theindication determined by the SMF can be sent together, and this may beused when the terminal generates a service request message later.

The indication for synchronization/asynchronization with the NASsignaling connection may be determined in the following method. First,the indication may be stored in a user data management (UDM) managingsubscription data of the UE, and the SMF may acquire the indication fromthe UDM in the PDU session establishment procedure. Second, theindication may be transferred to the SMF and the UE in a terminal policyincluding information on the indication in the PDU session establishmentprocedure or subsequently from a policy control function (PCF) takingcharge of the policy. Third, the UE may directly specify the indicationwhen it sends a PDU session establishment request message for the PDUsession establishment procedure. In this case, the SMF may finallydetermine the indication, and may transfer the information on thedetermined indication to the AMF and the UE.

Thereafter, if the terminal does not perform data transmission/receptionover a predetermined time, an N2 release procedure for releasing the NASsignaling connection is performed by the RAN or the AMF. By performing aservice request procedure by the network or the terminal with respect tothe terminal that has entered into the CM-IDLE state, the terminal maybe shifted from the CM-IDLE state to the CM-CONNECTED state.

In this case, with respect to the PDU session in which the indicationfor synchronization/asynchronization with the NAS signaling connectionis ON, the terminal may transmit the service request message in whichthe PDU session ID is not included through the NAS signaling. The AMFhaving received the service request message may perform a PDU sessionActivation procedure with respect to the session in which the indicationis ON based on the indication information stored together with theassociation between the PDU session ID managed by the AMF itself and theserving SMF ID. For the PDU session activation procedure, the AMF maysend a request message for setting up the UP connection of the sessionto the SMF managing the PDU session together with the PDU session ID.

Even in case where the service request procedure by the network isperformed with respect to the terminal in the CM-IDLE state, a similaroperation may be performed. In this case, the AMF transmits pagingthrough all RANs belonging to a location unit for tracking the terminal(e.g., tracking area list), and in response to this, the terminal havingreceived the paging sends a paging response. If the paging response isreceived, in the same manner as described above, the AMF may perform thePDU session activation procedure with respect to the session in whichthe indication is ON based on the indication information stored togetherwith the association between the PDU session ID managed by the AMFitself and the serving SMF ID.

If it is determined that the terminal is in a non-allowed area in whicha service related to the session is not allowed before the AMF transmitsto the SMF signaling for the PDU session Activation procedure withrespect to the PDU session in which the indication forsynchronization/asynchronization with the NAS signaling connection isON, the PDU session activation procedure may not be performed.

If data transmission/reception does not occur over the predeterminedtime with respect to the terminal that is in the CM-CONNECTED state, theRAN or the AMF may perform an N2 release procedure for releasing the NASsignaling connection. In this case, the AMF may perform a PDU sessiondeactivation procedure with respect to all SMF managing the PDU sessionfor the purpose of releasing the UP connection with respect to all thePDU sessions in which the indication is ON.

In addition, a case where an independent session deactivation procedureis supported for each PDU session with respect to the terminal that isin the CM-CONNECTED state may be considered. The deactivation procedureof releasing the UP connection for each session may be performed by theRAN, AMF, SMF, or an anchor UPF.

First, in case where the AMF triggers deactivation, it may operate notto request the PDU session deactivation from the SMF with respect to thesession in which the indication for synchronization/asynchronizationwith the NAS signaling connection of the PDU session ID managed by theAMF is ON. Next, in case where the SMF triggers deactivation, it may notdirectly perform the PDU session deactivation procedure since the SMFcan identify the indication for synchronization/asynchronization withthe NAS signaling connection for each session. Even in case where theRAN or the UPF performs triggering, it is possible to preventindependent session deactivation for the session in which the indicationfor synchronization/asynchronization with the NAS signaling connectionis ON by making the SMF not perform the PDU session deactivationprocedure.

Specifically, in case where a plurality of UPFs participate in aspecific PDU session of the terminal, the UP connection between theterminal and the anchor UPF taking charge of connection with an externaldata network (DN) may be composed of data radio bearer (DRB) between theUE and the RAN, N3 tunnel between the RAN and the UPF that is anend-point of an N3 tunnel, and an N9 tunnel between the UPF that is anend-point of the N3 tunnel and the anchor UPF that is an end-point of anN6 interface.

FIG. 2 illustrates a case where the terminal sets up two PDU sessions.The UP connection of the session is composed of the DRB and the N3tunnel since PDU session 1 is set up through one UPF (UPF3), whereas theUP connection of the session is composed of the DRB, the N3 tunnel, andthe N9 tunnel since PDU session 2 is set up through two UPFs (UPF1 andUPF2).

When releasing only the UP connection of the PDU session in case wherethe terminal is shifted from the CM-CONNECTED state to the CM-IDLE stateor the terminal supports an independent session deactivation procedurewith respect to a PDU session in which the UP connection is set upthrough a plurality of UPFs like the PDU session 2, the terminal mayrelease the DRB and the N3 tunnel, but may maintain the N9 tunnelbetween the UPFs without removing the same. This is because MO/MTtraffics to occur later can be rapidly transmitted and received throughthe corresponding PDU session.

In performing a PDU session establishment procedure including aplurality of UPFs, the SMF may request to receive a notification on a UElocation change from the AMF. The request may be implemented through amethod for subscribing the corresponding service in case where the SMFtransfers an indication for the notification to the AMF or the AMFprovides a service, such as a UE location notification.

The UE location information may be reported not only in a cell or basestation ID but also in the unit of an area that can be identified in acore network in order to grasp the location of the terminal, such as atracking area (TA). With respect to the requested session, the AMFreports the same when the UE location is changed.

The SMF having received the notification for the UE location perform aprocedure for identifying whether the UE location is included in theservice area of the UPF that is an end-point of the N3 tunnel, and if itis determined that the UE location is still included in the service areaof the UPF, the SMF maintains the N9 tunnel between the UPF and theanchor UPF of the PDU session. If the SMF does not directly manage theservice area of the UPF, it may identify whether the UE location belongsto the service area through a query to the UPF. If it is determined thatthe UE location is not included in the service area of the UPF, the SMFmay release the N9 tunnel. In this case, the SMF may newly set up the N9tunnel with the anchor UPF by newly selecting the end-point UPF of theN3 tunnel that is optimum to the UE location.

In addition, a management scheme related to the maintenance/release andchange of the N9 tunnel may be performed not only based on the UElocation information but also on other conditions. As an example, thePDU session may be allocated with a QoS profile (or parameter) includinga QoS requirements from the 5GC, and if the QoS profile is changed, theSMF may release the N9 tunnel or may newly configure the N9 tunnel bysetting up another new intermediate UPF (I-UPF).

The change of the QoS profile may include a notification from the RAN ora change of the QoS profile of the corresponding session through the UDMor the PCF. The QoS profile may have per session aggregate maximum bitrate (session-AMBR) and per UE aggregate maximum bit rate (UE-AMBR) foreach PDU session, and in case of a guaranteed bit rate (GBR) QoS flow,the QoS profile may include a guaranteed bit rate (GFBR) and a maximumflow bit rate (MFBR). Further, in case of the 5GC, a 5G QoS indication(5AI) may be configured to include a resource type (GBR or non-GBR), apriority level, a packet delay budget, and a packet error rate, and maymean the change of such values. The change of the QoS profile may beperformed through a PDU session modification procedure.

In addition, the management scheme related to the maintenance/releaseand change of the N9 tunnel may be performed through reception of aninput of a dynamic load state of the UPF constituting the N9 tunnel. Inparticular, in case where the SMF monitors the load state of the UPFsmanaged by the SMF itself, if the load of the intermediate UPF ratherthan the anchor UPF exceeds a specific threshold, the N9 tunnel of thePDU session using the intermediate UPF as a transmission path may bereleased, or the N9 tunnel may be newly configured by changing theintermediate UPF to a new intermediate UPF having low congestion (i.e.,having a load that is smaller than a threshold value). The dynamic loadstate of the UPF may be determined by the amount of data traffic passingthrough the corresponding UPF, the number of PDU sessions actually setup, and relative capacity between UPFs.

In addition, the management scheme related to the maintenance/releaseand change of the N9 tunnel may be performed based on capability orfunctionality of the UPF used in a specific session of the terminal. Asan example, the functionality/capability of the UPF to satisfy therequirements, such as data network name (DNN) used during the sessionsetup of the terminal, access point name (APN), network slice selectionassistance information (NSSAI), UE usage type, service and sessioncontinuity (SSC) mode, and service type. Through this, if it isdetermined that the intermediate UPF does not satisfy thefunctionality/capability, the SMF may maintain only the anchor UPF ofthe corresponding PDU session by releasing the N9 tunnel, or may newlyset up the N9 tunnel by selecting a new intermediate UPF satisfying thefunctionality/capability.

In addition, the management scheme related to the maintenance/releaseand change of the N9 tunnel may be performed through reception of aninput of a UE mobility pattern. As an example, the AMF of the 5GC maydirectly calculate the mobility pattern of the UE, or may acquire the UEmobility pattern from a third party server. If it is determined that theUE mobility is large beyond a specific threshold value (e.g., if thenumber of times of handover occurring during a specific time exceeds athreshold value), the AMF may notify the SMF of the UE mobilityinformation. Accordingly, the SMF may reduce a signaling load for N9tunnel update by releasing the N9 tunnel with respect to the PDU session(in which the UP connection is deactivated) of the UE, or may reduce thenumber of times of N9 tunnel update by setting up the existing anchorUPF and a new N9 tunnel through selection of a new intermediate UPFhaving a wider service area.

The information on the UE mobility pattern may be used to determinewhether to maintain or release the N9 tunnel between the intermediateUPF and the anchor UPF. Further, if the PDU session has a plurality ofanchor UPFs, the N9 tunnel may mean the N9 tunnel between theintermediate UPF existing at the end of the N3 tunnel that is thenext-hop of the base station and a branching point for branching thetraffic to the plurality of anchor UPFs or the intermediate UPF servingas an uplink classifier.

The PDU session in which the UP connection is set up through a pluralityof UPFs may be considered in a roaming scenario. In case of home-routedroaming as shown in FIG. 3, the N9 tunnel exists between the UPF of ahome PLMN (HPLMN) and the UPF of a visited PLMN (VPLMN), and the N9tunnel is always maintained regardless of the NAS signaling connectionstate of the terminal and the deactivation state of the PDU session. Inthis case, under the assumption that local offloading is permitted inthe VPLMN by the SMF of the HPLMN, another UPF may be additionallyinserted between the RAN and the UPF, and with respect to the N9 tunnelbetween the UPFs in a VPLMN network, the N9 tunnel maintenance andrelease schemes proposed according to the present disclosure may beapplied through signaling between the AMF and the SMF of the VPLMN.

Further, in case of local breakout roaming that is another roamingscenario, as shown in FIG. 4, the N9 tunnel maintenance and releasescheme proposed according to the present disclosure may be applied withrespect to the PDU session in which the N9 tunnel exists throughsignaling between the AMF and the SMF of the VVPLMN.

Hereinafter, the main operation according to the present disclosure willbe described through detailed embodiments.

In an embodiment, association including an indication forsynchronization/asynchronization with a PDU session ID, serving SMF ID,and NAS signaling connection managed by an AMF in case where a terminalsets up a plurality of PDU sessions will be described.

FIG. 5 shows a case where a terminal sets up three PDU sessions with thesame DN, and each PDU session configures an UP connection throughdifferent UPFs. In particular, if the PDU session including UPF1 iscalled number 1, the PDU session including UPF2 is called number 2, andthe PDU session including UPF3 is called number 3, PDU sessions 1 and 2are managed by SMF1, PDU session 3 is managed by SMF2, and the terminalis registered in a network by an AMF to perform mobility management.

Referring to FIG. 6, information on the PDU sessions managed by the AMFare included for a scenario of FIG. 5. A PDU session ID, a serving SMF,a PDU session status indicating activation/deactivation status of thecurrent UP connection, and an indication forsynchronization/asynchronization with a NAS signaling connectionproposed according to the present disclosure are indicated for each PDUsession. FIG. 6 shows an example in which PDU session 1 is synchronizedwith the NAS signaling connection. Accordingly, if the NAS signalingconnection is set up in PDU session 1, the UP connection of the PDUsession can be set up from the AMF to the SMF even if the terminal doesnot request the same.

Through an embodiment, the operation of each network entity related toan indication for synchronization/asynchronization with a NAS signalingconnection will be described. Referring to FIG. 7, an SMF may determinean indication for synchronization/asynchronization with the NASsignaling connection for each PDU session (S701), and if thesynchronization is determined, it becomes possible to transfer to an AMFand SMF the indication for synchronization/asynchronization with the NASsignaling connection can be transferred together with a PDU session IDcapable of identifying a PDU session (S702). Further, the SMF may storethe indication for synchronization/asynchronization with the NASsignaling connection in a PDU session context managed by the SMF itself(S703).

FIG. 8 shows an operation of an AMF related to an indication forsynchronization/asynchronization with the NAS signaling connection. Ifthe AMF receives the indication for synchronization/asynchronizationwith the NAS signaling connection together with a PDU session ID (S801),it may store the indication in a context related to the PDU sessionmanaged by the AMF itself (S802).

FIG. 9 illustrates a UE operation related to an indication forsynchronization/asynchronization with a NAS signaling connection. If UEreceives an indication for synchronization/asynchronization with a NASsignaling connection together with a PDU session ID in a similar mannerto the AMF (S901), it may store the indication in a context related tothe PDU session managed by the AMF itself (S902).

In an embodiment, when a NAS signaling connection state between aterminal and an AMF is changed, an AMF operation related to anindication for synchronization/asynchronization with a NAS signalingconnection is illustrated. Referring to FIG. 10, if the NAS signalingconnection state is shifted from a CM-CONNECTED state to a CM-IDLE state(S1001), the AMF identifies an indication forsynchronization/asynchronization with the NAS signaling connection foreach PDU session managed by the AMF itself with respect to the terminal(S1002), and if the indication exists, it may request an SMF thatmanages the PDU session to perform a PDU session deactivation procedure(S1003).

Referring to FIG. 11, if the NAS signaling connection state is shiftedfrom the CM-IDLE state to the CM-CONNECTION state (S1101), the AMFidentifies an indication for synchronization/asynchronization with theNAS signaling connection for each PDU session managed by the AMF itselfwith respect to the terminal (S1102), and if the indication exists, itmay request the SMF that manages the PDU session to perform a PDUsession activation procedure (S1103).

In an embodiment, the operation of UE related to an indication forsynchronization/asynchronization with a NAS signaling connection will bedescribed. In order for a terminal that is in a CM-IDLE state to beshifted to a CM-CONNECTED state, it may perform a service requestprocedure. The terminal may generate a service request message bydetermining whether to include a PDU session ID in accordance with anindication for synchronization/asynchronization with the NAS signalingconnection with respect to a PDU session already set up by the terminalitself.

Referring to FIG. 12, if MO data of a specific PDU session occurs(S1201), the terminal identifies the indication forsynchronization/asynchronization with the NAS signaling connection forthe corresponding PDU session, and if the indication exists (S1202), itmay not include a PDU session ID in a service request message (S1203).If the indication does not exist, the terminal may determine whether anUP connection of the corresponding PDU session is necessary in theservice request message, and if it is determined that the UP connectionis necessary, it may include the PDU session ID in the service requestmessage (S1204). The service request message may be transferred to theAMF through NAS signaling.

In an embodiment, if a plurality of UPFs participate in a process inwhich a terminal sets up a PDU session, an operation performed by an SMFwill be described. If the SMF determines that a plurality of UPFs arenecessary for an UP connection of a PDU session in a PDU sessionestablishment process, the SMF configures an N9 tunnel between the UPFs.

Referring to FIG. 13, when configuring the N9 tunnel (S1301), the SMFmay request to receive a notification on a UE location change from theAMF during the PDU session establishment process or after completion ofthe process (S1302). If a PDU session setup process remains, the SMF mayperform the remaining procedure (S1303). Thereafter, if the terminalenters into a CM-IDLE state, location information of the terminal may bemanaged by the AMF.

FIG. 14 illustrates an operation of an SMF in case where a terminal in aCM-IDLE state receives a notification on location information of theterminal from an AMF. If the SMF receives the notification on thelocation of the terminal from the AMF (S1401), it determines throughcomparison whether the terminal location is included in a service areaof an UPF that is an end-point of an N3 tunnel (S1402), and if theterminal location is included in the service area, it may maintain theN9 tunnel (S1403). However, if it is determined that the terminallocation deviates from the service area of the UPF that is an end-pointof the N3 tunnel, the SMF may release the N9 tunnel (S1404).

FIG. 15 illustrates an operation of an AMF in case where the AMFreceives a notification on UE location change from an SMF (S1501). TheAMF may transmit a notification message including information on alocation of new UE to the SMF having requested the notification on theUE location change whenever the UE location change occurs before thesubsequent corresponding session is released.

In an embodiment, a detailed procedure in which an AMF requests a PDUsession activation from an SMF if an indication forsynchronization/asynchronization with a NAS signaling connection existswith respect to the PDU session of a terminal will be described. Eachprocedure illustrated in FIG. 16 may be explained by the description inTable 1 below.

TABLE 1 1. The AMF sends PDU session activation request including PDUsession ID to the SMF associated with the PDU session via N11 message.2. The SMF sends N11 message to the AMF by containing N2 sessionrequest. The N11 message also contains the CN tunnel informationallocated by the UPF serving the PDU session and QoS informationassociated with the PDU session. 3. The AMF sends N2 session request tothe (R)AN including CN tunnel information and QoS information receivedfrom the SMF. 4. The (R)AN performs RRC Connection Reconfiguration withthe UE to establish (R)AN resources depending on the QoS information forthe PDU session to be activated. The (R)AN also allocates (R) AN tunnelinformation for the PDU session. Now, the uplink data from the UE can bedelivered to the UPF via the (R)AN. 5. The (R)AN sends N2 sessionrequest ack to the AMF including (R)AN tunnel information of theactivated PDU session. 6. The AMF forwards the N2 SM informationreceived from the (R)AN to the SMF via N11 message. 7a. The SMF providesN4 session modification request to the UPF by including (R)AN tunnelinformation received from the (R)AN. 7b. The UPF provides N4 sessionmodification response to the SMF.

More specifically, the AMF 163 generates and transfers a PDU sessionactivation signaling for setup of an UP connection of a PDU session tothe SMF 165 managing the corresponding PDU session through inclusion ofa PDU session ID in the PDU session in which the indication exists(S1601). If the PDU session activation signaling is received, the SMF165 performs a procedure for setup of the UP connection of thecorresponding PDU session. The SMF 165 may send a message including N3tunnel related information already set up in an anchor UPF 164 and QoSrelated information (QoS profile) of the corresponding session to a(R)AN 162 through the AMF 163 (S1602 and S1603). The (R)AN havingreceived the message for the setup of the UP connection of the PDUsession may allocate a necessary base station resource by performing anoperation including RRC connection reconfiguration together with the UE161 (S1604).

The N3 tunnel related information generated by the (R)AN 162 may betransferred again to the SMF 165 through the AMF 163 (S1605 and S1606).Then, the SMF 165 may transmit a session modification message includingthe N3 tunnel related information received from the (R)AN 162 tocomplete the N3 tunnel setup to an anchor UPF 164 of the correspondingsession (S1607 a and S1607 b).

In an embodiment, a case where a plurality of UPFs are included in a PDUsession establishment procedure by a terminal will be described. Asshown in FIG. 17, operation S1701 includes a process in which UE 171generates and transfers a new PDU session ID to an AMF 173 through NASsignaling in order to start a PDU session establishment. At operationS1702, the AMF 173 identifies that the PDU session ID is new from thereceived NAS message, and selects an SMF 175 for managing thecorresponding session. At operation 1703, the AMF 173 forwards a NASsignaling message to the selected SMF 175. At operations S1704 a andS1704 b, the SMF 175 acquires subscription information from a user datamanagement server (UDM) 176 in order to identify the subscriptioninformation for the session. This process may not be performed.

At operation S1705, the SMF 175 may select a plurality of anchor UPFs174 a and 174 b through UPF selection. Operations S1706 a, S1706B, S1707a, and S1707 b include a process of setting up sessions with a pluralityof UPFs newly selected. Operation S1708 illustrates a procedure in whichan SMF 175 sends signaling for session setup to the AMF 173. Thissignaling may include a NAS message to the UE 171 and an N2 message tothe (R)AN 172.

The NAS message may include a PDU session establishment accept and an IPaddress for session in case of an IPv4 session type, and the N2 messagemay include information on the N3 tunnel (e.g., tunneling ID) setup inthe anchor UPF 174 a at operation S1707 a and S1707 b.

Further, at operation S1708, if it is determined that the N9 tunnelsetup is necessary, the SMF 175 may transmit an N11 message including anindication for requesting a notification on the UE location to the AMF173. The AMF 173 having received the indication for the UE locationnotification may store this information in a session related contextmanaged by the AMF itself.

At operation S1709, the AMF 173 transfers the N2 message and NAS messageto the (R)AN 172, and the (R)AN 172 includes a process of setting up atunnel of the anchor UPF 174 a from the received N2 message. AToperation S1710, the (R)AN 172 includes a process of performing a DRBsetup for the session with the UE 171 and transferring the NAS messageto the UE 171. Through operation S1711, the (R)AN 172 includes a processof sending an ACK for signaling performed at operation S1709, includingthe N3 tunnel information set up by the (R)AN itself, to the AMF 173.

At operation S1712, the AMF 173 transfers the N3 tunnel informationreceived from the (R)AN 172 to the SMF 175, and at operation S1713, theSMF 175 transfers the N3 tunnel information generated by the (R)AN 172to UPF1 174 a that is an end-point of the N3 tunnel. Through this, theN3 tunnel setup for data transmission is completed. Through operationS1714, an anchor UPF 174 b acquires all tunnel related information forthe N9 tunnel setup to complete the N9 tunnel setup.

When all the UP connections for the session are completed through anoperation S1715, the signaling may be additionally sent to the AMF 173.If the SMF 175 does not request the notification on the UE location atprevious operation, it may request the notification from the AMF 173 atthis time. Thereafter, in case of an IPv6 PDU session type, the SMF 175may generate a router advertisement message including an IP prefixinformation newly allocated, and may transfer the message to the UE 171through UP signaling via the anchor UPF 174 b.

In an embodiment, if a terminal in a CM-IDLE state moves, an N9 tunnelrelease operation with respect to a PDU session composed of a pluralityof UPFs will be described. FIG. 18 illustrates a procedure related tothis embodiment. Operation S1801 includes a process in which an AMF 183transfers an N11 message to an SMF 185 that has requested the SMF 185 tonotify of a UE location change. Operation S1802 includes a process ofdetermining whether the UE belongs to a service area of UPF1 184 a basedon the UE location notified from the AMF 183, and a process of releasingan N9 tunnel previously set up if it is determined that the UE deviatesfrom the service area of the UPF1 184 a.

Through operations S1803 a, S1803 b, S1804 a, and S1804 b, the SMF 185exchanges signaling for releasing the N9 tunnel with the UPF1 184 a thatis an end-point of the N3 tunnel and UPF2 184 b that is an anchor UPF.In this case, for downlink data buffering, the SMF performs a sessionmodification process with the anchor UPF 184 b, and performs a sessionrelease process with the UPF1 184 a that is an end-point of the N3tunnel. In addition, if it is determined that the N9 tunnel setup isnecessary in a new UE location, the SMF 185 may perform a procedure ofselecting a UPF suitable to the new UE location and setting up theanchor UPF 184 b and the new N9 tunnel. If the N9 tunnel for the PDUsession is not newly set up, the SMF 185 may send an N11 messageincluding a message for requesting not to receive a notification on theUE location change any more from the AMF 183 (S1805).

FIG. 19 illustrates a procedure of setting up an anchor UPF and a new N9tunnel through selection of a UPF suitable to a new UE location.

More specifically, an AMF 193 transmits an N11 message for notifying anSMF 195 of a UL location (S1901), and the SMF 195 determines release ofan N9 tunnel for a PDU session based on this (S1902). Further, the SMF195 selects a UPF, and performs a PDU session modification procedurewith the anchor UPF at operations S1904 a and S1904 b.

Further, at operations S1905 a and S1905 b, the SMF 195 perform asession setup process with a newly selected UPF2 194 c, and atoperations S1906 a and S1906 b, the SMF 195 performs a session releaseprocess with the existing UPF1 194 a. Thereafter, the SMF 195 may notifythe AMF 193 of the UPF change through the N11 message (S1907).

In an embodiment, a procedure of performing N9 tunnelmaintenance/release and change in accordance with another condition inaddition to UE location information. As an example, the process mayinclude a change of a QoS profile allocated to a PDU session. Inaddition, a management scheme related to the maintenance/release andchange of the N9 tunnel may receive a dynamic load state of a UPFconstituting the N9 tunnel as an input to be performed. In addition, themanagement scheme related to the maintenance/release and change of theN9 tunnel may receive UPF functionality/capability as an input to beperformed. In addition, the management scheme related to themaintenance/release and change of the N9 tunnel may receive a UEmobility pattern as an input to be performed.

FIG. 20 is a diagram illustrating an operation for releasing an N9tunnel in case where an SMF receives a trigger condition for releasingthe N9 tunnel with respect to a PDU session composed of a plurality ofUPFs according to an embodiment.

More specifically, an SMF may receive a change of a trigger conditionfor UE in a CM-IDLE state (S2001). Based on this, the SMF may determinewhether to maintain an N9 tunnel for a PDU session (S2002). As anexample, the SMF may determine to maintain the N9 tunnel in accordancewith the changed trigger condition (S2003), and unlike this, the SMF maydetermine to release the N9 tunnel or to reestablish a new I-UPF and theN9 tunnel in accordance with the changed trigger condition (S2004).

FIG. 21 is a block diagram illustrating the SMF in a network accordingto an embodiment of the present invention.

As illustrated in FIG. 21, a SMF entity according to the presentdisclosure may include a transceiver 2110, a memory 2130 and acontroller 2120 coupled with the transceiver 2110 and the memory 2130.

In an embodiment, the controller 2120 is configured to control thetransceiver 2110 to transmit a first message, requesting a locationchange notification for a terminal in an idle state, to an access andmobility management function (AMF) entity, to receive a second message,including information on a changed location of the terminal, from theAMF entity. And, the controller 2120 is configured to determine whetherto maintain at least one of a plurality of user plane functions (UPFs)included in the PDU session for the terminal based on the secondmessage.

FIG. 22 is a block diagram illustrating the AMF in the network accordingto an embodiment of the present invention.

As illustrated in FIG. 22, an AMF entity according to the presentdisclosure may include a transceiver 2210, a memory 2230 and acontroller 2220 coupled with the transceiver 2210 and the memory 2230.

In an embodiment, the controller 2220 is configured to control thetransceiver 2210 to receive a first message, requesting a locationchange notification for a terminal in an idle state, from a sessionmanagement function (SMF) entity, and to transmit a second message,including information on a changed location of the terminal, to the SMFentity based on the first message if the location change of the terminalis detected, wherein the second message is used to determine whether tomaintain at least one of a plurality of user plane functions (UPFs)included in the PDU session for the terminal by the SMF entity.

FIG. 23 is a block diagram illustrating the terminal in the networkaccording to an embodiment of the present invention.

As illustrated in FIG. 23, a terminal according to the presentdisclosure may include a transceiver 2310, a memory 2330 and acontroller 2320 coupled with the transceiver 2310 and the memory 2330.

The transceiver 2310 may transmit/receive a signal to/from a basestation which communicates with the AMF/UPF of the SMF according to thepresent disclosure. The signal may include control information and data.Also, the controller 2320 may control a series of processes so that theterminal can operate according to the embodiments of the presentdisclosure.

Although embodiments of the present disclosure have been described inthe specification and drawings, these are merely used as generalmeanings to assist those of ordinary skill in the art to gain acomprehensive understanding of the present disclosure, and do not limitthe scope of the present disclosure. It will be apparent to those ofordinary skill in the art to which the present disclosure pertains thatvarious modifications are possible based on the technical concept of thepresent disclosure in addition to the embodiments disclosed herein.Further, if needed, the respective embodiments may be combined with eachother to be operated.

Although the present disclosure has been described with variousembodiments, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method performed by a session managementfunction (SMF) in a communication system, the method comprising:receiving, from a terminal, a first message including information on afirst protocol data unit (PDU) session; determining the first PDUsession for the terminal as a specific PDU session, the specific PDUsession for which a user plane connection being activated based on atransition from a connection management (CM)-idle state to aCM-connected state; transmitting, to the terminal, a second messageincluding an indication indicating the first PDU session being thespecific PDU session; identifying an inactivity of a second PDU sessionfor the terminal, in case that there is no data transfer for the secondPDU session; and performing a deactivation procedure of the second PDUsession, based on the inactivity of the second PDU session beingidentified, wherein a deactivation procedure of the first PDU sessionbased on an inactivity of the first PDU session is not performed.
 2. Themethod of claim 1, wherein the first message further includes a requestfor the specific PDU session, and wherein the first PDU session isdetermined as the specific PDU session based on the request.
 3. Themethod of claim 1, wherein the first message is a PDU sessionestablishment request message, and wherein the second message is a PDUsession establishment accept message.
 4. The method of claim 1, whereinthe first PDU session is deactivated, in case that the terminal entersthe CM-idle state.
 5. The method of claim 4, further comprising:receiving, from the terminal, a service request for the second PDUsession, wherein a user plane connection for the second PDU session isactivated based on the service request, wherein the terminal in theCM-idle state enters into the CM-connected state, based on an activationof the user plane connection for second PDU session, and wherein a userplane connection for the first PDU session is activated based on theterminal entering into the CM-connected state.
 6. A method performed bya terminal in a communication system, the method comprising:transmitting, to a session management function (SMF), a first messageincluding information on a first protocol data unit (PDU) session; andreceiving, from the SMF, a second message including an indicationindicating the first PDU session being a specific PDU session, thespecific PDU session for which an user plane connection being activatedbased on a transition from a connection management (CM)-idle state to aCM-connected state, wherein a deactivation procedure of a second PDUsession for the terminal is performed based on an inactivity of thesecond PDU session, in case that there is no data transfer for thesecond PDU session, and wherein a deactivation procedure of the firstPDU session based on an inactivity of the first PDU session is notperformed.
 7. The method of claim 6, wherein the first message furtherincludes a request for the specific PDU session, and wherein the firstPDU session is determined as the specific PDU session based on therequest.
 8. The method of claim 6, wherein the first message is a PDUsession establishment request message, and wherein the second message isa PDU session establishment accept message.
 9. The method of claim 6,wherein the first PDU session is deactivated, in case that the terminalenters the CM-idle state.
 10. The method of claim 9, further comprising:transmitting, to the SMF, a service request for the second PDU session,wherein a user plane connection for the second PDU session is activatedbased on the service request, wherein the terminal in the CM-idle stateenters into the CM-connected state, based on an activation of the userplane connection for second PDU session, and wherein a user planeconnection for the first PDU session is activated based on the terminalentering into the CM-connected state.
 11. A session management function(SMF) in a communication system, the SMF comprising: a transceiver; anda controller configured to: receive, from a terminal via thetransceiver, a first message including information on a first protocoldata unit (PDU) session, determine the first PDU session for theterminal as a specific PDU session, the specific PDU session for which auser plane connection being activated based on a transition from aconnection management (CM)-idle state to a CM-connected state, transmit,to the terminal via the transceiver, a second message including anindication indicating the first PDU session being the specific PDUsession, identify an inactivity of a second PDU session for theterminal, in case that there is no data transfer for the second PDUsession, and perform a deactivation procedure of the second PDU session,based on the inactivity of the second PDU session being identified,wherein a deactivation procedure of the first PDU session based on aninactivity of the first PDU session is not performed.
 12. The SMF ofclaim 11, wherein the first message further includes a request for thespecific PDU session, and wherein the first PDU session is determined asthe specific PDU session based on the request.
 13. The SMF of claim 11,wherein the first message is a PDU session establishment requestmessage, and wherein the second message is a PDU session establishmentaccept message.
 14. The SMF of claim 11, wherein the first PDU sessionis deactivated, in case that the terminal enters the CM-idle state. 15.The SMF of claim 14, wherein the controller is further configured toreceive, from the terminal via the transceiver, a service request forthe second PDU session, wherein a user plane connection for the secondPDU session is activated based on the service request, wherein theterminal in the CM-idle state enters into the CM-connected state, basedon an activation of the user plane connection for second PDU session,and wherein a user plane connection for the first PDU session isactivated based on the terminal entering into the CM-connected state.16. A terminal in a communication system, the terminal comprising: atransceiver; and a controller configured to: transmit, to a sessionmanagement function (SMF) via the transceiver, a first message includinginformation on a first protocol data unit (PDU) session, and receive,from the SMF via the transceiver, a second message including anindication indicating the first PDU session being a specific PDUsession, the specific PDU session for which an user plane connectionbeing activated based on a transition from a connection management(CM)-idle state to a CM-connected state, wherein a deactivationprocedure of a second PDU session for the terminal is performed based onan inactivity of the second PDU session, in case that there is no datatransfer for the second PDU session, and wherein a deactivationprocedure of the first PDU session based on an inactivity of the firstPDU session is not performed.
 17. The terminal of claim 16, wherein thefirst message further includes a request for the specific PDU session,and wherein the first PDU session is determined as the specific PDUsession based on the request.
 18. The terminal of claim 16, wherein thefirst message is a PDU session establishment request message, andwherein the second message is a PDU session establishment acceptmessage.
 19. The terminal of claim 16, wherein the first PDU session isdeactivated, in case that the terminal enters the CM-idle state.
 20. Theterminal of claim 19, wherein the controller is further configured totransmit, to the SMF via the transceiver, a service request for thesecond PDU session, wherein a user plane connection for the second PDUsession is activated based on the service request, wherein the terminalin the CM-idle state enters into the CM-connected state, based on anactivation of the user plane connection for second PDU session, andwherein a user plane connection for the first PDU session is activatedbased on the terminal entering into the CM-connected state.